The basic process for preparing quick-rehydrating rice products is described in U.S. Pat. No. 2,438,939 to Ozai-Durrani. According to that disclosure, rice is first cooked in water to substantially gelatinize the starch and raise the moisture content of the rice grains to cause substantial swelling of the grains. The swollen grains are then dried by circulating air at a temperature of up to about 140.degree. C., through the grains. The hot air dries the grains in their enlarged condition by causing the exterior to dry first and harden. The enlarged or swollen rice grains are easier to hydrate. Products made by this process have enjoyed substantial commercial success, but are costly to produce.
In United Kingdom Patent Specification No. 563,792, there is described a process for cooking cereals, such as rice, for the preparation of a quick-rehydrating product. According to this disclosure, the cereal is steeped and steamed in a single vessel; however, this is a batch process. There is no recognition therein that decreased energy usage, decreased product solids losses, and time savings could be achieved in preparing a fully gelatinized rice of high quality, by continuously moving the rice through cooking and steaming zones simultaneously maintained within the same enclosed vessel.
There have been efforts to run various processes and unit operations continuously in a variety of rice processes. For example, U.S. Pat. No. 3,261,690 to Wayne, employs screw conveyors to mill rice as well as convey it to various processing units. Also, U.S. Pat. Nos. 2,498,573, 2,525,137, 2,592,407, 2,758,031, 2,801,176, and 3,085,011 disclose employing separate screw conveyors for each of the processing steps of soaking, steaming and drying the rice. Simple conveying of rice by screw conveyor is also disclosed. However, none of these references recognized that substantial efficiencies and savings could be obtained in the preparation of a fully gelatinized rice by carrying out both the cooking and steaming steps in the same vessel with continuous movement of the rice from a water cooking zone to a steaming zone.
The use of pressure cookers employing continuous screw conveyors is known for steam peeling potatoes, steaming oysters, and the like processes; however, their use with water in a first zone to cook a potentially sticky product such as rice and then steam in a second zone within the same enclosed chamber is unknown.